(a) Field of the Invention
The present invention relates to a system and method for reducing the effects of multi-path fading and signal interference in a system using orthogonal codes and binary signal values. More specifically, the present invention relates to a maximum likelihood detection (MLD) system and method that reduces the complexity of MLD and improves performance in the system using orthogonal codes and binary signal values.
(b) Description of the Related Art
The modulation/demodulation methods for supporting a data transfer rate increasing in a confined frequency band include the quadrature amplitude modulation (QAM) method. The QAM modulation method may enhance the data transfer rate because the amount of information increases with an increase in the constellation, but it has a problem in regard to its mobility and application for 16-QAM or greater with a separation of more than a predetermined value. Namely, the QAM method is susceptible to the effect of distortion because the redundancy of noise decreases with an increase in the constellation. That is, the QAM modulation method has a trade-off relationship between information and noise.
It is known that the channel capacity of channels having a rich scattering characteristic is proportional to the number of transceiver antennas in the same bandwidth. Hence, studies have been done on a method for detecting received signals using a multiple input/multiple output (MIMO) antenna system with a plurality of antennas so as to increase channel capacity. But this method is known to have a problem in regard to its implementation, because the mobile terminal concerned is required to have a plurality of antennas and a rich scattering characteristic for channels.
In addition, there has been recently suggested a method for increasing data transfer rate without an increase in the entire bandwidth for users by using an intrinsic spreading code and orthogonal codes. But this method, which utilizes binary values, has problems in regard to overcoming the effects of multipath fading or signal interference and the complexity of MLD calculations according to the length of the spreading code.